1. Field of the Invention
The present invention relates generally to a headlamp mounted on an automotive vehicle or the like. More particularly, the present invention relates to a vehicular headlamp including a single filament for radiating a light beam therefrom exclusively for passing-by vehicles.
2. Description of the Related Art
A conventional headlamp of the foregoing type has been typically disclosed in an official gazette of Japanese Laid-Open Patent NO. 64-14801 (corresponding to Japanese Patent Application NO. 62-170620) which was filed by the common applicant to the present invention. According to the prior invention, an auxiliary reflective mirror is arranged for the headlamp including double filaments, i.e., a filament for radiating a light beam therefrom for the purpose of normal running and a filament for radiating light beam therefrom for passing-by vehicles.
In the past era when the foregoing prior invention was filed with the Patent Office in this country, a four lamp type headlamp including two lamps of type 1 and two lamps of type 2 was officially approved by the Transportation Ministry in this country. Specifically, the lamps of type 1 are used for radiating light beam therefrom for the purpose of normal running and the lamps of type 2 are used such that a light beam for the purpose of normal running is changed to a light beam for passing-by vehicles and vice versa during running of a vehicle. When the vehicle runs in a suburb at a high speed, both lamps of type 1 and type 2 are turned on but when the vehicle runs on streets in a city at a low speed, the lamps of type 2 only are turned on with a light beam for passing-by vehicles. Accordingly, in that era, there was no industrial requirement for mounting on a vehicle a headlamp adapted to radiate a light beam therefrom exclusively for passing-by vehicles.
However, as time elapses, things vary. In recent years, a simplified four lamp type headlamp has been officially approved by the Transportation Ministry wherein lamps of type 1 are used for radiating a light beam exclusively for the purpose of running and lamps of type 2 are used for radiating a light beam exclusively for passing-by vehicles. When the vehicle runs with a light beam exclusively for a passing-by vehicle, the lamps of type 2 only are turned on and when the vehicle runs with light beam for the purpose of normal running, the lamps of type 1 are turned on in addition to the filaments of type 2. Thus, there has arisen a new industrial requirement for providing a headlamp adapted to radiate a light beam therefrom exclusively for passing-by vehicles. However, it has been found that the hitherto known technology can not meet the foregoing requirement satisfactorily.